EXPERIMENTAL INVESTIGATION OF THE EFFECTS OF FLUID HETEROGENEITY UPONTHE MOTION OF RIGID ELLIPSOIDAL INCLUSIONS DURING BULK INHOMOGENEOUS SHORTENING

An experimental study of the motions of rigid ellipsoidal inclusions w ithin deforming homogeneous and heterogeneous fluid systems indicated that the time behaviour of such objects, measured relative to the expe rimental apparatus, can vary significantly between the two system type s during inhomogeneous time-dependent flow. Initially aligned ellipsoi dal inclusions within a deforming homogeneous fluid were rotated in th e sane sense as an adjacent passive strain marker. Introduction of het erogeneity, by partially enclosing the ellipsoidal inclusions with a l ess viscous fluid, resulted in three different rigid-body behaviours d uring deformation. The behaviours observed for initially aligned ellip soids in the system containing fluid heterogeneities were: (1) opposit e-sense rotation to that of the strain marker; (2) negligible rotation of the objects; and (3) same sense of rotation as that of the strain marker. A computerized, time-based, analysis of the deformation, possi ble through the incorporation of marker particles into each of the two different deforming systems, revealed similar deformation kinematics for the two experimental types at both the system and sub-system scale . Results of the experiments indicate that significant differences can occur in rigid-body behaviour between apparently similarly deforming homogeneous and heterogeneous systems. The results suggest that fluid flow theory, as derived for rigid-body behaviour in homogeneous fluids , may be unsuitable for the purpose of qualitatively predicting rigid- object behaviour within deforming rock systems that are highly anisotr opic al the porphyroblast/porphyroclast scale. This notion is supporte d by an examination of the assumptions and simplifications upon which the theory relating to rigid-body behaviour in homogeneous fluids was originally based. (C) 1997 Elsevier Science Ltd.